catheter-mediated defibrillator pulses

Factors affecting bubble formation during delivery of defibrillator pulses to arrhythmogenic cardiac tissue via a catheter are unknown. We investigated the role of energy, electrode surface area, interelectrode distance, and electrode polarity on bubble formation and on current and voltage waveforms during delivery of damped sinusoidal discharges from a standard defibrillator to anticoagulated bovine blood. Gas composition was studied with mass spectrometry. Defibrillator energy settings were varied between 5 and 360 J. The principal catheter used for study was a Medtronic 6992A lead. Additional electrodes tested included 2, 5, and 10 mm long No. 6F, 7F, and 8F copper electrodes. Interelectrode distances used to assess the effect of anode-cathode spacing were 1, 5, 10, and 20 cm. Bubble volume increased linearly from 0.043 to 0.134 ml per cathodal pulse and from 0.030 to 3.50 ml per anodal pulse as energy settings were increased from 5 to 360 J (r = .99). Typical smooth waveforms for both current and voltage were seen only in the absence of bubbles. The voltage waveform was distorted for each cathodal pulse of 100 J or more and for each anodal pulse of 10 J or more only if bubbles were present. The effect of electrode surface area on bubble formation was tested at a 200 J energy setting and at a 10 cm interelectrode distance with the use of cathodal pulses. Bubble formation varied inversely with electrode surface area (r = .876). Bubble formation, however, varied minimally as interelectrode spacing was changed from 1 to 20 cm. The effect of polarity on bubble formation when the Medtronic 6992A distal electrode and an 8.5 cm disk electrode separated by 10 cm were used was highly significant. For a 200 J pulse, bubble formation with the catheter as anode was 3.30 + 0.10 ml and with the catheter as cathode it was 0.070 + 0.002 ml (p < .001). Mass spectrometry of both anodal and cathodal gas samples demonstrated the constituents of the gas bubble to include a variety of gases, which is inconsistent with simple electrolytic production of the bubbles observed. The predominance of nitrogen in either polarity sample suggested that the principal source of the bubble was dissolved air. In summary, bubble formation at an electrode receiving damped sinusoidal outputs from a standard defibrillator does not vary significantly with varying interelectrode distance. However, it is directly proportional to energy and inversely proportional to electrode surface area. Anodal catheter discharges produce considerably more bubbles than do cathodal discharges. Distortions in the voltage waveform correlate with physical factors leading to high-pressure shockwave generation and to subsequent extrusion of dissolved gases from solution. Circulation 73, No. 3, 525-538, 1986. GAS EMBOLIZATION is a potential concern after delivery of catheter-mediated defibrillator pulses to cardiac tissue.1-' This issue is most relevant when pulses are delivered in the left ventricular cavity for From the Divisions of Cardiology and Cardiac Surgery, The University of Washington, Harborview Medical Center, Seattle. Supported in-part by the American Heart Association, Washington Affiliate, and by the Seattle Medic I-Emergency Medical Services Foundation. Address for correspondence: Gust H. Bardy, M.D., Harborview Medical Center, 325 Ninth Ave., Seattle, WA 98104. Received May 31, 1985; revision accepted Nov. 29, 1985. Dr. Coltorti is a recipient of a fellowship grant from the Ministero della Pubblica Istruzione, Italy. Clif Alferness is manager of research, Physio-Control, Inc. Vol. 73, No. 3, March 1986 ablation of ventricular tachycardia foci.4`8 Bubble formation in this chamber might embolize to the coronary arteries or to the systemic circulation, raising questions regarding the safety of the present technique, especially in view of previous work in dogs that has suggested that 0.1 to 0.2 ml of air embolized into the coronary artery is sufficient to result in myocardial damage.9 To determine whether potentially hazardous gas volumes could be generated in the heart during catheter-mediated defibrillator pulses, we investigated several factors in vitro that might influence gas formation. The factors investigated included: defibrillator energy, electrode size or surface area, interelectrode spacing, 525 by gest on A ril 6, 2017 http://ciajournals.org/ D ow nladed from